[L]ong-term romantic relationships start to look more like friendships. The emotions are no less intense, but the structure of the relationships might take on the characteristics of friendships today: Constantly-changing groups of people whose feelings for each other range from talk-every-day closeness to casual meetups at the pub. Stability will be provided by the network, and by a few long-term close connections ...

The third possibility is "neo-courtly love": marriages revert to being social/business transactions between families, and spouses look outside the home to find passion and romance.

The first scenario seems the most immediately plausible to me, but all three make for interesting thought experiments. Best of all, Newitz's post offers a list of novels and authors that explore each of these ideas, making it a handy, sci-fi-inflected companion piece to
Double X'
s guide to beach book reading
.